1. Field of the Invention
The present invention relates in general to a transfer machine for machining workpieces transferred on a transfer line by a plurality of machining units disposed along the transfer line. More particularly, it relates to a flexible transfer machine of the type wherein each of machining units disposed along a transfer line is capable of performing on each workpiece transferred thereto a machining operation which depends upon the kind of the workpiece.
2. Description of the Prior Art
Where plural kinds of workpieces are machined by a transfer machine which disposes a plurality of machining units in positions to correspond respectively to machining stations on a transfer line, the kinds of machining operation cycles performed at each machining station are different from one another to a small extent, depending upon the kinds of workpieces selectively transfrred thereto. It is therefore necessary to identify the kind of a workpiece transferred to each machining station and to perform an appropriate machining operation corresponding to the identified workpiece kind.
A transfer machine has been known which is capable of identifying the kind of a workpiece transferred to each machining station, by shifting workpiece kind identification signals synchronously with the shifting motion of the workpieces on the transfer line. In this known transfer machine, where the kinds of workpieces to be machined therein reaches more than several-tens in number, a problem is raised in that a controller used therein becomes complicated in circuit construction, or that where such a controller is constituted by a sequence controller of a stored program type, then a stored program prepared therefor becomes very complicated.
More specifically, the plural kinds of workpieces machined by the known transfer machine are similar to one another. Therefore, even where more than fifty kinds of workpieces are processed by the transfer machine, it is usual that the kinds of workpieces machined at each machining station are several to seven or eight at most. In this case, the selection of a machining cycle appropriate to each workpiece kind must be made by a dedicated controller provided at each machining station. However, because programmable sequence controllers used as such a dedicated controller do not have a function to lead its processing operation to various points on a sequence program given thereto depending upon the result of comparison operations, the sequence program would be made voluminous if an attempt is made to discriminate more than fifty workpiece identification codes from one another in accordance with the sequence program for the purpose of selecting an appropriate machining cycle based upon a discriminated one of the identification codes. This would disadvantageously result not only in making the programmable sequence controllers for machining control increased in size, but also in making the programming of the sequence program very troublesome.